1. Field of the Invention
The present invention relates to sockets for electronic parts and, more particularly, to a two-point contact type socket having contacts that are simultaneously brought into contact with upper and lower surfaces of a terminal of an electronic equipment such as a large-scale integrated circuit (LSI).
2. Description of the Related Art
In recent years, many flat-package type LSIs are used in portable electronic equipments such as a digital camera, etc. Since the flat-package type LSI having fine pitch terminals has a small electric contact area, a contact failure tends to occur when conducting an electric test. Thus, a two-point contact socket is used, which permits a stable electric test of a flat-package type LSI (for example, refer to the following patent documents 1 trough 4).
Especially, in an LSI socket (sample table) used for a final test or a characteristic evaluation test of an LSI, an electric contact portion between the LSI and the socket is getting smaller. However, as a bad effect, there is a problem in that a test failure occurs or a characteristic evaluation must be done again due to a bad contact. The cause of such a bad contact is that it tends to receive influences of dirt and dust adhering on a contact surface, a spot on a contact surface or a deformation of a terminal due to a reduction in the contact area caused by the terminals being arranged with a fine pitch. Thus, the contact of a two-point contact structure is used, which contacts with terminals of an LSI by sandwiching the terminals from both vertical directions.
[Patent Document 1]
Japanese Laid-Open Patent Application No. 2001-357951 (FIGS. 5–7)
[Patent Document 2]
Japanese Laid-Open Patent Application No. 2004-103432 (FIGS. 1–6)
[Patent Document 3]
Japanese Laid-Open Patent Application No. 2003-157939 (FIG. 2, FIG. 8, FIG. 9)
[Patent Document 4]
Japanese Laid-Open Patent Application No. 2003-303653 (FIGS. 1–6)
Recently, the number of signal terminals of a flat-package type LSI is increasing to 100–200. With such a development in making the fine pitch structure, it is apparent that a possibility of occurrence of contact failure with respect to supply of an electric current is increased more. In many cases, a second contact piece to be brought into contact with an upper side of an LSI terminal is made of a conductive material piece (single piece lead) formed by mold forming. However, a pitch between LSI terminals has been made smaller, and, thereby, it has become difficult to arrange the second contact pieces on the upper sides of the LSI terminals at an equal interval (pitch). Additionally, even if the second contact pieces are arranged at an equal interval, a pitch variation may occur due to a mechanical action such as an elastic deformation of the second contact pieces, which causes a problem in that adjacent contact pieces short-circuit with each other.
Moreover, in a current two-point contact type socket, the upper contact piece to be brought into contact with an LSI terminal from an upper side deforms and displaces when making a contact, and, thus, degradation with passage of time occurs in the upper contact piece. Accordingly, it is necessary to conduct a maintenance operation such as a replacement when degraded with passage of time. Thus, it is desirous to develop a two-point contact type socket having a structure in which all upper contact pieces can be replaced at once.
Furthermore, since the upper side contact piece of the current two-point contact type socket uses a spring property which elastically deforms while drawing a trajectory, a socket structure is in consideration of a space for allowing a deformation of the upper contact piece, which causes a problem in that the socket itself is very large. Thus, it is desirous to develop a two-point contact type socket which is smaller than a current one and an operation of the contact piece therein is simple.